Method for transmitting a signal via a power line network, transmitter, receiver, power line communication modem and power line communication system

ABSTRACT

A method for transmitting signals over a power line network, wherein within the power line network at least one transmitter and at least one receiver communicate via at least two channels, each channel including a respective feeding port of at least one transmitter and the respective receiving port of the at least one transmitter and transmitter including at least two feeding ports. The method: determines a channel characteristic of each of the channels; applies a feeding port selection criterion based on the channel characteristic; and selects an excluded feeding port among the at least two feeding ports based on the feeding port selection criterion, wherein the excluded feeding port is not used during further communication. A corresponding power line communication modem can implement the method.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/601,772, filed Aug. 31, 2012, which is a continuation of U.S.application Ser. No. 13/412,279, filed Mar. 5, 2012, now U.S. Pat. No.8,442,127, which is a continuation of U.S. application Ser. No.12/595,265, filed Oct. 9, 2009, now U.S. Pat. No. 8,160,162. The entirecontents of each of which are incorporated herein by reference. U.S.application Ser. No. 12/595,265 is the National Stage of PCT/EP08/06212,filed Jul. 28, 2008 and is based upon and claims the benefit of priorityfrom prior European Patent Application No. 07016489.2, filed Aug. 22,2007.

DESCRIPTION

The invention relates to a method for transmitting signals via a powerline network, a transmitter and a receiver. The invention relates aswell to a power line communication modem and a power line communicationsystem.

BACKGROUND

Power line communication (PLC), also called mains communication, powerline transmission (PLT), broadband power line (BPL), power band or powerline networking (PLN), is a term describing several different systemsfor using power distribution wires for simultaneous distribution ofdata. A carrier can communicate voice and data by superimposing ananalogue signal over the standard 50 Hz or 60 Hz alternating current(AC). For indoor applications PLC equipment can use household electricalpower wiring as a transmission medium.

In order to increase the bandwidth of PLC systems it has been proposedto use multiple-input−multiple-output schemes (MIMO) which are knownfrom wireless communication systems.

It is an object of the invention to further increase the bandwidth ofPLC systems.

The object is solved by a method for transmitting a signal, atransmitter, a receiver, a power line communication modem and a powerline communication.

Further embodiments are defined in the dependent claims.

Further details of the invention will become apparent from aconsideration of the drawings and ensuing description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows steps of one embodiment of the invention,

FIG. 2 a shows a block diagram of a transmitter according to a furtherembodiment of the invention,

FIG. 2 b shows a block diagram of a receiver according to a furtherembodiment of the invention,

FIG. 3 shows a block diagram of a power line communication systemaccording to a further embodiment of the invention,

FIG. 4 shows a block diagram of a conventional power line communicationsystem,

FIG. 5 shows a power line communication system according to a furtherembodiment of the invention,

FIG. 6 shows steps of a further embodiment of the invention,

FIG. 7 shows steps of a further embodiment of the invention,

FIG. 8 shows a schematic block diagram to explain the function of atransmitter according to a further embodiment of the invention,

FIG. 9A shows a circuit diagram for impedance modulating devices,

FIG. 9B shows a schematic diagram of the time-dependence of the voltage,when impedance modulating devices are present,

FIG. 9C shows a schematic diagram of a voltage-time relation with partsof similar channel capacities to explain a further embodiment of theinvention,

FIG. 10 shows steps of a further embodiment of the invention, and

FIG. 11 shows a block diagram of a power line communication systemaccording to a further embodiment of the invention.

DETAILED DESCRIPTION

In the following, embodiments of the invention are described. It isimportant to note that all described embodiments in the following andtheir properties and technical features may be combined in any way, i.e.there is no limitation that certain described embodiments, propertiesand technical features may not be combined with others.

In FIG. 1 in a step S100 a channel characteristic is determined and in apower line network a transmitter and at least one receiver communicatevia at least two channels, each of said channels having a respectivefeeding port of said at least one transmitter and a respective port ofsaid at least one transmitter and said transmitter having at least twofeeding ports. A corresponding power line network is depictedschematically in FIG. 3 that will be explained below.

The channel characteristics may be derived from a channel estimation anddescribe the channel by, for instance, bit-error-rate (BER) orsignal-to-noise-ratio (SNR). Other channel characteristics may be thepower or the energy of the received signal on said channel.

In a step S102 a feeding port selection criterion is applied based onthe channel characteristic determined in step S100. While applying thefeeding port selection criteria the channel characteristics of differentchannels are compared in order to decide, which feeding port or feedingports would be used, since the best reception is ensured while usingthese feeding ports.

In a step S104 an excluded feeding port is selected among the at leasttwo feeding ports based on the feeding port selection criteria, whereinthe excluded feeding port is not used during further communication.

According to Kirchhoff's Rule in PLC systems in presence of three wiresor conductors there are only two independent feeding possibilities.

In step S104 the feeding port is selected based on the feeding portselection criterion, thereby identifying the worst channelcharacteristics. Since the channel is quasi-static for PLC systems, theselection of the feeding port remains stable until there is a dedicatedchange in the PLC network topology (for instance a light has beenswitched on or a device has been plugged or unplugged).

A channel capacity C of a channel might be calculated as

$C = {{B \cdot \frac{1}{N}}{\sum\limits_{i = 1}^{N}{\log_{2}\left( {\det\left( {I_{N_{R}} + {{\frac{1}{n_{T}} \cdot S}\; N\;{R \cdot H_{i} \cdot H_{i}^{H}}}} \right)} \right)}}}$with: B being the bandwidth of the channel, N being the number of OFDMsub-carriers, n_(R) being the number of receive ports, I_(NR) being then_(R)×n_(R) identity matrix, n_(r) being the number of transmit ports,SNR being the signal-to-noise ratio, H being the n_(R)×n_(R) channelmatrix.

Alternatively, in an adaptive OFDM-(orthogonal frequency divisionmultiplexing)-system, a channel equalizer within the receiver providesinformation about the signal-to-noise-ratio (SNR) for each sub-carrierof the OFDM system. Depending on the SNR condition on each sub-carrier,a suited constellation size is selected. The less SNR is available, themore robust the constellation has to be. As an example, for quadratureamplitude modulation (QAM), different constellations with a differentSNR requirement exist.

${constellation} \in \left\{ \begin{matrix}{B\; P\; S\; K} & {1\mspace{14mu}{bit}\text{/}{symbol}} \\{Q\; P\; S\; K} & {2\mspace{14mu}{bits}\text{/}{symbol}} \\{16\text{-}Q\; A\; M} & {4\mspace{14mu}{bits}\text{/}{symbol}} \\{64\text{-}Q\; A\; M} & {6\mspace{14mu}{bits}\text{/}{symbol}} \\{256\text{-}Q\; A\; M} & {8\mspace{14mu}{bits}\text{/}{symbol}} \\{1024\text{-}Q\; A\; M} & {10\mspace{14mu}{bits}\text{/}{symbol}} \\\ldots & \ldots\end{matrix} \right.$

Finally, the overall bit loading of one OFDM symbol can be taken asqualitative capacity criteria. The higher the total number of bits forone OFDM symbol (as a sum over all N sub-carriers), the higher thecapacity C:

$C \propto {\sum\limits_{i = 1}^{N}{constellation}_{i}}$

In case of MIMO, there are equalizers for all different receiving portsM. In this case, the overall sum of all channel equalizers can be takenas feeding port selection criterion:

$C \propto {\sum\limits_{m = 1}^{M}{\sum\limits_{i = 1}^{N}{constellation}_{m,i}}}$

In a further embodiment a period of an alternating current on said powerline network is divided at least into a first and a second part. A firstchannel characteristic is determined for the first part and a secondchannel characteristic is determined for the second part. Then a firstexcluded feeding port is selected for said first part based on saidfeeding port selection criteria and a second excluded feed is selectedfor said second part based on said feeding port selection criteria. Ifimpedance-modulating devices are present in the power line network themain impedance changes depending on the line cycle duration anddepending on the number of impedance modulating devices. When the numberof impedance modulating devices is not changing, the impedance changesare periodic with the line cycle duration, e.g. 20 ms for a 50 Hzalternating current. The impedance changes have dramatic influence todata transmission over power line. An impedance change during a databurst results in wrong channel equalization values after the impedancechange and causes non-correctable transmission errors. Therefore it isproposed to place the burst in time intervals where the impedance keepsstable. In presence of impedance-modulating devices the feedingselection is performed separately for each impedance condition so thatthe excluded feeding port change with different impedance settings. Thefeeding port selection can include an additional port selectioncriterion. Feeding ports, which are at least faced to impedancemodulating behavior, may be determined, since not every feeding pointcombination is faced to the same level of impedance modulation.

According to a further embodiment a respective channel capacity based onthe channel characteristics for said channel is determined and anexcluded channel with the channel capacity below a predeterminedthreshold is determined which is not used during further communicationafterwards.

Within this embodiment not only the feeding ports are determined butalso singular channels may be excluded from further communication. Thismight be useful in case of impedance modulating devices or in case ofimpulsive noise on the power line network.

In a further embodiment the channel characteristics of the channel isdetermined by transmitting an OFDM test signal via a plurality ofchannels simultaneously and determining a respective plurality ofchannel capacities for said plurality of channels based on the receivedversion of said OFDM test signal.

According to a further embodiment a multiple-input—multiple-outputcoding scheme (MIMO-scheme) is set based on the respective channelcapacities. By setting an appropriate MIMO in data throughput andreliability of the PLC system is further optimized. Depending on thechannel characteristics and/or the bandwidth demand of the application,an appropriate MIMO coding scheme is selected. Available MIMO modes aretested sequentially and the best MIMO mode regarding throughput and/orbit error rate is chosen. In further embodiments the data transmissionis optimized regarding maximum throughput and/or transmissionreliability. For instance, Alamouti MIMO is designed in a way to achievebetter bit error rates (BER) performance without increasing thethroughput rate (special code rate is one). On the other hand, multiplexMIMO systems like HBLAST (Horizontal Bell Laboratories LayeredSpace-Time), VBLAST (Vertical Bell Laboratories Layered Space-Time) orEigenbeamforming-MIMO are designed to maximize the data throughput whileBER performance optimization on the physical layer is not the primaryfocus (special code rate is two).

In FIG. 2 a a block diagram of a transmitter 200 is depicted. Thetransmitter 200 comprises two feeding ports 202, 204 each of which isconfigured to feed signals into at least two channels and a processor206 configured to select an excluded feeding port of said at least twofeeding ports 202, 204 based on a determination of channelcharacteristics of said at least two channels, said processor 206 beingfurther configured to not use channels of said at least two channelsduring communication which are fed by said excluded feeding port (202 or204).

With respect to the wording “transmitter” and “receiver” it should beemphasized that within this description “transmitter” and “transmittingmodem” as well as “receiver” and “receiving modem” are usedinterchangeably, since a power line communication modem forbidirectional communication comprises a transmitter as well as areceiver. Thus, in a power line system the communication of payload databetween power line communication modems is performed between atransmitting modem (i.e. the transmitter) and a receiving modem (i.e.the receiver).

In a further embodiment the processor 206 might be further configured toexclude channels with the channel capacity below the predeterminedthreshold from further communication and the processor 206 might beconfigured to set a multiple-input multiple-output coding scheme basedon the respective channel capacities.

In FIG. 2 b a block diagram of a receiver 250 is depicted. The receiver250 comprises at least one receiving port 252, which is the receivingend of at least two channels from the power line communication network,the channels being fed by at least two different feeding ports (notdepicted). The receiving port 252 is connected to a channel estimationunit 254, which is configured to determine channel characteristics ofsaid at least two channels. A processor 256 is connected to said channelestimation unit 254 and is configured to select the feeding port, whichshould be excluded from further communication based on the determinationof the channel characteristics from the channel estimation unit 254. Atransmitting unit 258 is connected to the processor 256 for transmittingan information about the excluded feeding port to a transmitter, whichafterwards only uses non-excluded feeding ports for the communicationwith the receiver 250.

Thus, the identification of the excluded feeding port might be performedin the receiver 250 or in the transmitter 200 depending on theinformation which is fed back to the transmitter. If the channelcharacteristics are fed back from the receiver 250 to the transmitter200, then within the transmitter the excluded feeding port is selected.If the receiver 250 already selects the excluded feeding port, then onlyan information about the excluded feeding port has to be fed back to thetransmitter 200.

In FIG. 3 a schematic block diagram of a power line communication system300 is depicted, which comprises a transmitter 302 and a receiver 304.The transceiver 302 might be part of a power line communication modem305 and the receiver 304 might be part of a further power linecommunication modem 306. The transceiver transmits signals to thereceiver 304 among a plurality of channels 307 wherein each of theplurality of channels 307 has a feeding port FP1, FP2, or FP3 and areceiving port RP1, RP2, RP3, or a RP4. In the depicted example withthree feeding ports FP1, FP2, FP3 and four receiving ports RP1, RP2,RP3, RP4 both possible channels 306 might be used for transmitting asignal from the transmitter 302 to the receiver 304.

In FIG. 4 the conventional power line communication system 400 isdepicted with a transmitting PLC modem 402 and a receiving PLC modem404. The transmitting PLC modem 402 and the receiving PLC modem 404 areconnected via power lines P, N, PE and a corresponding power linenetwork 406. The wires which represent the power line network are aphase line P, a neutral line N and a protective earth line PE. Inconventional power line communication schemes only one feeding port isused, i.e. the feeding of signals between the phase P and the neutralline N and also only one receiving port RP1 is used while receiving thesignal between the phase line P and the neutral line N at the receiver404.

When using also the protective earth line PE—as it is depicted in FIG. 4for a further embodiment of the power line communication system 500—itis possible for a transmitting PLC modem 502 to transmit a signal to areceiving PLC modem 504 via any combination of the phase line P, theneutral line N and the protective earth line PE. Thus, in total threefeeding port possibilities FP1, FP2, FP3 are present, namely a firstfeeding port FP1 where the transmitted signal is sent via the phase lineP and the neutral line N, a second feeding port FP2 where the signal issent between the phase line P and the protective earth line PE and athird feeding port FP3 where the signal is sent between the neutral lineN and the protective earth line PE. On the receiver side there are afirst receiving port RP 1 evaluating a received signal between the phaseline P and the neutral line N, a second receiving port RP2 evaluating asignal received between the phase line P and the protective earth PE anda third receiving port RP3 evaluating a signal received between theneutral line N and the protective earth line PE. A fourth receiving portRP4 is also available, which describes the reception via a so-calledcommon mode (CM). CM signals are created unintentionally at unbalancednetworks. Unbalanced parasitic capacities from installations or devicesto ground cause a CM current returning to the source. Due toelectro-magnetic coupling between neighbored wires, cross talk arises,i.e. the transmit signal from any feeding port is visible on all fourreception ports RP1, RP2, RP3, RP4.

FIG. 6 shows a message sequence chart for the feeding port selectionprocess. At the beginning the transmitting modem 600 selects in a stepS602 the first (out of three) feeding possibilities and indicates thisby a control message in a step S604 to the receiving modern 606. Suchcontrol messages might be handled in upper layers of any OSI layersystem (e.g. a medium access layer (MAC) or even a data link controllayer (DLC)). The receiving modem 606 acknowledges this request In astep S608 and waits for the start of the test transmission. Thetransmitting modem 600 starts the capacity test of the transmissionpossibility of the first feeding port 1 in a step S610 and sends acorresponding test signal in a step S612. In case the receiving modem606 knows the length of a test transmission (e.g. a certain number ofdata bursts) it starts automatically to calculate the channel capacityas channel characteristic after the test sequence is received in a stepS614. The result of the capacity calculation is sent back to thetransmitter 600 in a step S616.

The steps are repeated for the other two remaining feedingpossibilities. In a step S620 the transmitting modern 600 selects thesecond feeding possibility and indicates this by a control message in astep S622 to the receiving modem 606. The receiving modem 606acknowledges this request in a step S624 and waits for the start of thenext test transmission. The transmitting modem 600 starts the capacitytest of the second feeding port FP2 in a step S626 and sends acorresponding test signal in a step S628. The receiving modem 606calculates the channel capacity for this second feeding possibility in astep S630 and reports the capacity back to the transmitting modem 600 ina step S632.

In a step S634 the transmitting modem 600 selects the third feedingpossibility and indicates this by a control message in a step S636 tothe receiving modem 606. The receiving modem 606 acknowledges thisrequest in a step S638 and waits for the start of the next testtransmission. The transmitting modem 600 starts the capacity test of thethird feeding port FP3 in a step S640 and sends a corresponding testsignal in a step S642. The receiving modem 606 calculates the channelcapacity for this second feeding possibility in a step S644 and reportsthe capacity back to the transmitting modem 600 in a step S646.

After all three test transmissions are finished; the transmitting modem606 starts to send regular data bursts in a step S650.

In FIG. 7 an alternative scheme for testing the channels is depicted. Incase a fixed length of the test sequences is used, i.e. a receivingmodem 706 knows the length of the test transmission from thetransmitting modem 700, the handshaking to signal the start of the testsequence can be omitted. Thus, in a step S702 the transmitting modem 700signals to the receiving modem 706 that a signal feed test is requested.In a step S704 the receiver 706 acknowledge the feed test request to thetransmitter 700. In a step S708 the transmitter 700 selects the firstfeeding possibility and starts the capacity test directly for the firstfeeding port FP1 in a step S710. The test signal is transmitted in astep 712 and the receiving modem 706 calculates the capacity in a stepS714. The channel capacity is reported back to the transmitter 700 in astep S716.

These steps are repeated for all feeding possibilities. In a step S720the transmitting modem 700 selects the second feeding possibility andstarts the capacity test directly for the second feeding port FP2 in astep S722. The test signal is transmitted in a step 724 and thereceiving modem 706 calculates the capacity in a step S726. The channelcapacity is reported back to the transmitting modem 700 in a step S728.

In a step S730 the transmitting modem 700 selects the first feedingpossibility and starts the capacity test directly for the third feedingport FP3 in a step S732. The test signal is transmitted in a step S734and the receiving modem 706 calculates the capacity in a step S736. Thechannel capacity is reported back to the transmitting modem 700 in astep S738.

Afterwards the transmitting modem 700 selects the best feedingpossibilities and starts the transmission in a step S740.

In FIG. 8 the block diagram of the transmitting PLC modem 800 isdepicted in order to explain how to switch between the different feedingports in the transmitter 800. Depending on the results of the feedingport selection mechanism, two of the available three ports are selectedfrom the two MIMO transmitting paths 802, 804 with the help of aswitching mechanism 806. MIMO transmitting path 802 and MIMOtransmitting path 2 804 are never set to the same position within theswitching mechanism 806. Within this embodiment the first transmittingpath 802 is using P-N as feeding port and the second transmitting pathis Using P-PE as feeding port.

FIG. 9A shows a circuit diagram and FIG. 9B shows a corresponding timedependence of the voltage UA on a power line, if impedance modulatingdevices are present. Mobile phone chargers and other charging devicesconvey in the circuitry that has the following properties:

-   -   If the capacity C charges, HF-signals from mains are shortcut.    -   If the diode is blocking, the rectifier has high input        impedance.

So the mains impedance changes at least twice within a line cycleduration.

The periodic impedance changes have dramatic influence to datatransmission over power line. An impedance change during a data burstresults in wrong channel equalization values after the impedance changeand causes non-correctable transmission errors. Therefore it isimportant to place the burst in time intervals where the impedance keepsstable, which is a task for a medium access control (MAC) layer of apower line communication system.

In FIG. 9C it is depicted that depending on the line cycle frequency,different channel conditions result in different feeding port selectionsand/or different MIMO schemes (in this example: two different channelconditions, but all different channel conditions might be possible aswell). The Y-axis represents the voltage UA of an AC line cycle.

In FIG. 10 steps for determining an appropriate MIMO coding scheme isdepicted. After the operation has been started in step 1000, the channelcharacteristics are determined in a step S1002. Afterwards in a stepS1004 it is investigated whether the signal-to-noise-ratio SNR is belowa certain threshold. If the answer is yes in a step S1006 a stable, biterror rate (BER)—optimized MIMO coding is selected, for example, anAlamouti MIMO scheme. If the signal-to-noise-ratio is above a certainthreshold it is determined whether significant disturbances are presentin the power line network in a step S1008. If a significant disturbanceis present then in a step S1006 a stable, bit error rate optimized MIMOcoding like Alamouti MIMO is used for the transmission as well. If thereare no disturbances in the power line network then in a step S1010 athroughput optimized MIMO coding, like HBLAST, VRLAST orEigenbeamforming-MIMO is selected. Afterwards in a step S1012 thetransmitter is informed about the selection which selection should beused afterwards in a regular operation in a step S1014. Thus, dependingon the channel characteristics, and/or the bandwidth demand of theapplication, an appropriate MIMO coding is selected.

In order to determine the quality of the channel, an initial phasebefore regular operation is proposed. During this initial phase thepower line communication channel is examined for disturbances (impedancemodulating or impulsive noise). All available MIMO schemes are testedsequentially. The best MIMO mode regarding throughput and/or bit errorrate might be chosen.

In FIG. 11 a further embodiment for a power line communication system1100 is depicted. In the power line communication system 1100 a firstnode 1102 is connected via a first channel 1104 with a second node 1106and via a second channel 1108 with a third node 1110. The second node1106 and the third node 1110 are connected via a third channel 1112. Asan example an impulsive noise source 1114 disturbs the third channel1112 between the second node 1106 and the third node 1110.

Since the selection of the MIMO mode might be performed for eachconnection between all nodes, 1102, 1106, 1110 in the network 1100,different connections between different nodes might choose differentMIMO modes depending on the connection conditions. In the exampledepicted in FIG. 11 the communication between the first node 1102 andthe second node 1106 on the first channel 1104 with a short distance hasa good signal-to-noise-ratio SNR without any disturbance. Thus, athroughput optimized MIMO can be chosen. On the third channel 1112between the second node 1106 and the third node 1110 there is adisturbance present, resulting from the impulses of the noise source1114. Thus, even if there is only a short distance between the secondnode 1106 and the third node 1110 the bit error rate optimized MIMO(e.g. Alamouti) is selected. Between the first node 1102 and the thirdnode 1110 there is a long distance on the second channel 1108 but nodisturbance is present. A bit error rate optimized MIMO (e.g. Alamouti)might be selected in order to overcome a bad SNR due to the longdistance.

Due to the quasi-static behavior of power line communication channelsthe process to determine the optimized MIMO mode might be performed whena new node enters the network (and again if the channel conditionschange fundamentally). It is proposed how to select the best possiblefeeding ports for MIMO communication over power line communicationchannels. The channel characteristics for different feeding ports aremeasured for all transmission possibilities and the port with the worstchannel characteristics is excluded from further communication. Inaddition it has been prevented how to deal with impedance modulatingdevices in order to choose the appropriate feeding ports for differentparts of an alternating current.

What is claimed is:
 1. A Power Line Communication (PLC) transmitterconnectable to phase, neutral, and protective earth wires of a powerline network, the PLC transmitter comprising: a first feeding port thatis connectable to the phase and neutral wires and that is configured tooutput a first communication signal for transmission from thetransmitter; a second feeding port that is connectable to the phase andprotective earth wires or to the neutral and protective earth wires andthat is configured to output a second communication signal fortransmission from the transmitter; circuitry configured to perform afeeding port selection operation, based on a determination of presenceof a disturbance of the power line network, for output of at least oneof the first communication signal and the second communication signal,for data transmission, via at least one of the first feeding port andthe second feeding port, respectively, based on the feeding portselection operation; and transmitting circuitry that transmits data viaa selected feeding port, the transmitted data being at least one of thefirst communication signal and the second communication signal, whereinthe disturbance of the power line network is a periodic impedance changebased on line cycle duration.
 2. The transmitter according to claim 1,wherein the feeding port selection operation selects for exclusion forthe data transmission a feeding port and corresponding pair of wires. 3.The PLC transmitter according to claim 2, wherein the circuitry isconfigured to select the feeding port to be excluded and correspondingpair of wires based on channel capacity of one or more correspondingchannels being below a predetermined threshold.
 4. The PLC transmitteraccording to claim 2, wherein the selected feeding port to be excludedis the other of the first and second feeding ports not controlled by thecircuitry for output of the data transmission.
 5. The PLC transmitteraccording to claim 2, wherein the PLC transmitter is configured totransmit information identifying the selected feeding port to beexcluded to a receiver.
 6. The PLC transmitter according to claim 2,wherein the circuitry is configured to keep selected for exclusion theselected feeding port and corresponding pair of wires until a topologychange in the power line network.
 7. The PLC transmitter according toclaim 1, wherein the circuitry is configured to select the selectedfeeding port for data transmission based on information fed back from aPLC receiver.
 8. The PLC transmitter according to claim 1, furthercomprising a third feeding port that is connectable to the other one ofthe phase and protective earth wires or the neutral and protective earthwires and that is configured to output a third communication signal, thethird communication signal being a differential mode signal.
 9. The PLCtransmitter according to claim 1, wherein the circuitry is configured tokeep selected the selected feeding port until a topology change occursin the power line network.
 10. The PLC transmitter according to claim 1,wherein upon determination, by the circuitry, that the disturbance ispresent, a bit error rate optimized MIMO coding is selected for the datatransmission, and upon determination, by the circuitry, that thedisturbance is not present, a throughput optimized MIMO coding isselected for the data transmission.
 11. The PLC transmitter according toclaim 1, wherein a plurality of MIMO modes are tested sequentially bythe PLC transmitter, and a MIMO mode from the plurality of MIMO modeswith a best performance regarding at least one of throughput and biterror rate is selected.
 12. The PLC transmitter according to claim 1,wherein the circuitry is configured to control output of at least one ofthe first communication signal and the second communication signal basedon a received signal from a receiver indicating that one of the feedingports is to be excluded in the data transmission, the circuitryperforming the feeding port selection operation based on the receivedsignal.
 13. A method for transmitting signals via a power line network,the method comprising: selecting as a feeding port for data transmissionfrom a Power Line Communication (PLC) transmitter, using a processor,one of a first feeding port and a second feeding port of the PLCtransmitter based on whether or not a disturbance is detected in thepower line network; and transmitting data via the selected feeding port,the transmitted data being one of a first communication signal and asecond communication signal, wherein the disturbance is a periodicimpedance change based on line cycle duration.
 14. The method accordingto claim 13, wherein said selecting includes selecting one of the firstand second feeding ports and corresponding pair of wires for exclusionin the data transmission.
 15. The method according to claim 14, whereinsaid selecting the feeding port for exclusion is performed responsive toa detected change in topology in the power line network.
 16. The methodaccording to claim 14, wherein the selected feeding port for exclusionis the other of the first and second feeding ports not selected for saidtransmitting data.
 17. The method according to claim 13, wherein saidselecting is based on information fed back from a PLC receiver, theinformation fed back from the PLC receiver identifying one of thefeeding ports and corresponding wires to be excluded in the datatransmission.
 18. A Power Line Communication (PLC) transmitterconnectable to a power line network, the PLC transmitter comprising:circuitry configured to select at least one of a first feeding port anda second feeding port of the PLC transmitter for output of datatherefrom based on detection of a disturbance of the power line network;and transmit data via a selected feeding port, the transmitted databeing at least one of the first communication signal and the secondcommunication signal, wherein the disturbance of the power line networkis a periodic impedance change based on line cycle duration.